1. Field of the Invention
The present invention generally relates to a memory system, and more particularly, to methods of calculating a compensation voltage and adjusting a threshold voltage according to error bit information, a memory apparatus, and a controller.
2. Description of Related Art
Along with the widespread of digital cameras, cell phones, and MP3 in recently years, the consumers' demand to digital storage media has increased drastically. Flash memory is one of the most adaptable storage media to be carried around and used for storing digital files due to its many characteristics such as data non-volatility, low power consumption, small volume, and non-mechanical structure. A solid state drive (SSD) is a storage device which uses a flash memory as its storage medium, and SSD has been broadly applied in computer systems as the master hard disc.
Existing flash memories can be categorized into NOR flash memories and NAND flash memories. The NAND flash memories can be further categorized into multi-level cell (MLC) NAND flash memories and single-level cell (SLC) NAND flash memories according to their different storage modes. In a SLC NAND flash memory, each memory cell stores one bit, while in a MLC NAND flash memory, each memory cell stores two or more bits.
Generally speaking, when data is read from or written into a specific memory cell in a memory cell array constructed with bit lines and word lines, other memory cells will be disturbed and accordingly the writing threshold voltages of these memory cells will be changed. In addition, wear caused by long-time idling, memory electric leakage, or repeated erasing or programming operations may also change the writing threshold voltages of the memory cells. As a result, errors may be produced when previously written data is read.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.